1. Field of the Invention
The present invention relates generally to a method of establishing and releasing a SCH (Supplemental channel) in a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a method of directly transitioning from an active state to an idle state when an SCH is released.
2. Description of the Related Art
CDMA has been developed to IMT-2000 standards which provide services like transmission of high quality voice and moving pictures and Internet browsing as well as the conventional service of voice transmission.
Data transmission occurs in bursts, with idle states without any data transmission often occurring in the mobile communication system. The idle states are a control hold state, a suspended state, and a dormant state. The IMT-2000 mobile communication system assigns a dedicated channel only if data transmission occurs in a data communication service. Further, it additionally provides a packet data service in which SCHs are designated as dedicated to transmit a large amount of packet data. To do so, SCHs have high variable data rates.
In consideration of limited radio resources, base station capacity, and the power consumption of a mobile station, a dedicated traffic channel (DTCH) and a control channel are connected only while data is being transmitted and the DTCH is released if data transmission is discontinued for a predetermined time period. Communication is made on the common channel while the dedicated channel is released, to thereby increase use efficiency of radio resources. For this purpose, call processing is comprised of different states according to channel assignment and the presence or absence of channel status information.
FIG. 1 is a state transition diagram for the packet service in a general mobile communication system.
Referring to FIG. 1, there are an active state 101, a control hold state 103, a suspended state 105, and a dormant state 107 for the packet service.
In the active state 101, input data is transmitted on a DTCH. Once a data service object connects a service option and initially enters the active state 101, a dedicated data channel is available and a base station and a mobile station performs initialization operations for RLP (Radio Link Protocol) and PPP (Point to Point Protocol). If data is not transmitted for a predetermined time period T—Active in the active state 101, the DTCH is released and the control hold state 103 is entered. If a non-data transmission period of longer than T—Active is expected based on an estimate of the amount of data that will be generated, a transition occurs from the active state 101 directly to the suspended state 105 or the dormant state 107, without passing through the control hold state 103.
In the control hold state 103, the base station and the mobile station preserve information about the service option, the RLP, and the PPP, and a dedicated control channel (DCCH) has been established. If transmit data is generated within a predetermined time T—Hold, the data service object reestablishes the DTCH to transmit the data and returns to the active state 101. On the other hand, if there is no transmit data until T—Hold elapses, the DCCH is released and the suspended state 105 is entered. The control hold state 103 is also transitioned directly to the dormant state 107 without passing through the suspended state 105 if a non-data transmission period is expected to be longer than T—Hold based on an estimated amount of data that will be generated.
In the suspended state 105, a fundamental channel (FCH), being a dedicated physical channel assigned to each mobile station, or the DCCH is released. Therefore, logical channels, the DCCH and the DTCH, are released. The mobile station communicates with the base station over a common signaling channel (CSCH) established on physical channels shared by a plurality of mobile stations, a paging channel and an access channel. The base station and the mobile station still preserve the information about the service option, the RLP, and the PPP in the suspended state 105. If user data is generated within a predetermined time T—Suspended in the suspended state 105, the data service object reestablishes the DCCH and the DTCH concurrently and returns to the active state 101. On the contrary, if no data is generated for T—Suspended, the data service object transitions to dormant state 107.
In the dormant state 107, the service option is disconnected and the link-layer connection is held between an IWF (internetworking function) and the mobile station only in the data service. All dedicated logical channels are released and communication is conducted on common channels in this state. Upon request of data service in the dormant state 107, the service option is to connected, the DTCH and the DCCH are re-established, and the active state 101 is entered.
In summary, the DTCH, the DCCH, and the service option are connected in the active state 101, the DCCH and the service option are connected in the control hold state 103, only the service option is connected in the suspended state 105, and only the link layer connection is held between the IWF and the mobile station in the dormant state 107.
As stated above, SCHs are utilized in order to provide the high speed packet data service in the CDMA mobile communication system. As compared to a control channel or an FCH, an SCH transmits only user data and a DCCH or a fundamental channel (FCH) must be set up before the SCH is assigned. Hence, the SCH is set up only in the active state 101 as shown in FIG. 1. In other words, the active state 101 must be entered to exchange SCH messages. Even when the SCH is to be released due to the absence of pack data, another idle state must be transitioned to, with the active state 101 interposed.
FIG. 2 illustrates the signal flow in a basic call set-up process, i.e., transition to the active state to set up a channel when a mobile station requests a call in the CDMA mobile communication system.
Referring to FIG. 2, the mobile station transmits an origination message requesting establishment of a dedicated channel to a base station on a reverse access channel (R-ACH) in step 201. Upon receipt of the origination message, the base station transmits a channel assignment message to the mobile station on a forward paging channel (F-PCH) in step 202. At the same time, the base station transmits null traffic on a channel with a corresponding orthogonal code. Upon receipt of the channel assignment message, the mobile station analyzes the null frame on the corresponding channel. If the mobile station confirms that the channel is successfully established, it transmits a preamble on its unique code channel to synchronize its timing to the base station during channel assignment in step 203. If bidirectional dedicated channels are successfully established, the base station transmits an acknowledgment (Ack) order in step 204. Upon receipt of the Ack order, the mobile station discontinues transmission of the preamble and becomes capable of transmitting a message on a DTCH (an FCH or a control channel).
In steps 205 to 208, service negotiations for the current available transmission environment are carried on between the base station and the mobile station to provide quality service to the users. After the negotiations are over, the channel assignment procedure ends in step 209.
FIGS. 3A and 3B are signal flows in SCH establishment and release procedures in the active state, separately upon request of a mobile station and upon request of the network.
Referring to FIG. 3A, the mobile station 301 generates an SCH request message to the base station 303 in step 701, as constructed below in Table 1.
TABLE 1FieldLength (bits)SIZE_OF_REQ_BLOB4REQ_BLOB8 × SIZE REQ BLOBUSE_SCRM_SEQ_NUM1SCRM_SEQ_NUM0 or 4REF_PN0 or 9PILOT_STRENGTH0 or 6NUM_ACT_PN0 or 3
If NUM_ACT_PN is included, the mobile station 301 shall include NUM_ACT_PN occurrences of the following record:
ACT_PN_PHASE15ACT_PILOT_STRENGTH 6NUM_NGHBR_PN0 or 3
If NUM_NGHBR_PN is included, the mobile station 301 shall include NUM_NGHBR_PN occurrences of the following record:
NGHBR_PN_PHASE15 NGHBR_PILOT_STRENGTH6RES_INFO_INCL1CH_IND0 or 3BLOB0 or 7
If the mobile station 301 wants the packet service, it transmits the SCH request message to the base station 303 on a traffic channel (a control channel or an FCH). The REQ_BLOB field shown in Table 2 indicates the use duration of the requested SCH.
Upon receipt of the SCH request message, the base station 303 checks physical resources for SCHs. If there is an available SCH, the base station transmits an SCH assignment message to the mobile station 301 in step 702. If the mobile station 301 operates in accordance with an IS-95B protocol, the SCH assignment message is generated in the format shown in Table 2.
TABLE 2FieldLength (bits)USE_RETRY_DELAY1RETRY DELAY0 or 8REV_INCLUDED1
Only if REV_INCLUDED is set to ‘1’, the following record is included:
REV_DTX_DURATIONEXPL_REV_START_TIME4REV_START_TIME1USE_REV_DURATION0 or 6REV_DURATION1USE_REV_HDM_SEQ0 or 8REV_SINKED_HDM_SEQ1NUM_REV_CODES0 or 2USE_T_ADD_ABORT3USE_SCRM_SEQ_NUM1SCRM_SEQ_NUM1REV_PARMS_INCLUDED0 or 4T_MULCHAN1BEGIN_PREAMBLE0 or 3RESUME_PREAMBLE0 or 30 or 3FOR_INCLUDED1
Only if FOR_INCLUDED is set to ‘1’, the following record is included:
FOR_SUP_CONFIG2EXPL_FOR_START_TIME1FOR_START_TIME0 or 6USE_FOR_DURATION1FOR_DURATION0 or 8USE_FOR_HDM_SEQ1FOR_LINKED_HDM_SEQ0 or 2
Only if FOR_INCLUDED is set to ‘1’ and FOR_SUP_CONFIG is set to ‘10’ or ‘11’, the following fields and records are included.
NUM_SUP_PILOTS3NUM_FOR_SUP3
Only if FOR_INCLUDED is set to ‘0’ and FOR_SUP_CONFIG is set to ‘10’ or ‘11’, NUM_SUP_PILOTS occurrences of the following record are included.
PILOT_PN9EXPL_CODE_CHANE1
If EXPL_CODE_CHAN is set to ‘1’, NUM_FOR_SUP occurrences of the following field are included for each PILOT_PN.
SUP_CODE_CHAN0 or 8
If EXPL_CODE_CHAN is set to ‘0’, the following field is included.
BASE_CODE_CHAN0 or 8
Upon receipt of the SCH assignment message, the mobile station 301 transmits data on the SCH in step 703. After transmitting the intended data, the mobile station 301 transmits an SCH release request message to the base station 303 in step 704. The SCH release request message is generated in the same format as shown in Table 1, except that an SCH release code is in the REQ_BLOB field. At present, the SCH, the FCH, and the DCCH are established. That is, the base station 303 and the mobile station 301 are in the active state 101. Upon receipt of the SCH release request message, the base station 303 transmits an SCH release message to the mobile station 301 in step 705 and releases the SCH in step 706. Since the FCH and the DCCH are still connected, the base station 303 and the mobile station 301 remain in the active state 101.
Referring to FIG. 3B, when packet data is generated from the network (not shown), the base station 303 transmits the SCH assignment message to the mobile station 301 in step 708. Upon receipt of the SCH assignment message, the mobile station 301 transmits data on an assigned SCH in step 709. The base station 303 and the mobile station 301 are in the active state and at present, the SCH, the FCH, and the DCCH are established. If no more data is generated from the network, the base station 303 transmits the SCH release message to the mobile station 301 in step 710 and releases the SCH in step 711. The FCH and the DCCH are still connected between the base station 303 and the mobile station 301. Therefore, the base station 303 and the mobile station 301 remain in the active state 101, despite the absence of transmit data. To transition to the control hold state 103, the suspended state 105, or the dormant state 107, the mobile station 301 and the base station 303 must carry on negotiations. That is, the SCH is released and the active state 101 is continued. Transition to another state occurs by exchanging messages for the transition between the mobile station 301 and the base station.
As described above, although the SCH is released, the FCH or the DCCH is still connected, i.e., the active state 101 is continued. In this state, if no user data is transmitted on either of the FCH and the DCCH, it is preferable that the active state 101 transitions to the control hold state 103, the suspended state 105, or the dormant state 107 as soon as possible to increase the use efficiency of radio resources.
In the typical CDMA mobile communication system, when data transmission on the SCH is discontinued, the active state is kept on. For transition to the control hold state, the suspended state, or the dormant state, the mobile station and the base station must exchange messages associated with the state transition. Therefore, radio resources are occupied despite discontinued data transmission.